The popularity of audio and video delivery and playback over the internet has increased significantly in the past years. Some causes of this increase are new compression techniques, the ease with which media player software can be provided as part of a webpage and the exponential increase in bandwidth and storage. Most of this delivery is uncoordinated and ad-hoc, and there is little to no reporting of what content is shared by whom.
It is desirable to keep track of which audio and video content is popular, i.e. is downloaded and/or viewed, at any moment in time. A single website or file sharing network may be able to report items that are popular on that particular site, but aggregating those popularity indicators is difficult. In addition, audio and video can appear on different websites or file sharing networks under different names and/or in edited forms.
Watermarking is a well-known technique for embedding identifiers in content. With the right watermarking algorithm, the identifier can be extracted from the content even after this content has been processed in several different manners, such as resizing, adding a logo, removing frames and so on. Each player would need a watermark detector that extracts the identifier and reports it to the central server. From this the central server can retrieve the right metadata and count the reported item into its popularity statistics. Extracting watermarks is however a resource-consuming operation. In addition, using watermarks to identify content only works when someone has previously inserted the watermark in the content. To day only a small subset of all content is available with watermarked identifiers.
An alternative to watermarking is called robust fingerprinting or robust hashing. With robust fingerprinting it is possible to identify content by matching perceptually relevant features from the content against features of known content in a database. This works for any content, even after modifications such as resizing, adding logos, encoding in a different format and so on. No actions comparable to embedding a watermark are necessary. In this manner, it is possible to add to each player (client) a fingerprinting subroutine that fingerprints every content item that is played and reports this fingerprint to the central server.
WO 2004/010353-A1 discloses a method of sharing multimedia objects such as audio or video, in particular in the context of file sharing networks. The method includes registering usage information relating to such sharing, such as the number of times a multimedia object has been shared, how long the multimedia object lasts, and so on. In an embodiment the multimedia object is identified by having the device that shares the object obtain a digital fingerprint for the object and retrieve associated metadata from a central server. Another embodiment uses watermarks for the same purpose.
This approach however has serious problems with bandwidth and processing power on both server and client. The client must extract an identifier from a watermark in the content or compute a digital fingerprint of every content item and send this identifier or fingerprint to the central server to obtain its associated metadata. Or, alternatively, the client must send a short fragment of audio to the server so that the server can extract the watermarked identifier or calculate a fingerprint for the content, allowing the server to obtain the metadata.